UsbRequest

public class UsbRequest
extends Object

java.lang.Object
   ↳ android.hardware.usb.UsbRequest


A class representing USB request packet. This can be used for both reading and writing data to or from a UsbDeviceConnection. UsbRequests can be used to transfer data on bulk and interrupt endpoints. Requests on bulk endpoints can be sent synchronously via UsbDeviceConnection.bulkTransfer(UsbEndpoint, byte[], int, int) or asynchronously via queue(ByteBuffer) and UsbDeviceConnection.requestWait(). Requests on interrupt endpoints are only send and received asynchronously.

Requests on endpoint zero are not supported by this class; use UsbDeviceConnection.controlTransfer(int, int, int, int, byte[], int, int) for endpoint zero requests instead.

Summary

Public constructors

UsbRequest()

Public methods

boolean cancel()

Cancels a pending queue operation.

void close()

Releases all resources related to this request.

Object getClientData()

Returns the client data for the request.

UsbEndpoint getEndpoint()

Returns the endpoint for the request, or null if the request is not opened.

boolean initialize(UsbDeviceConnection connection, UsbEndpoint endpoint)

Initializes the request so it can read or write data on the given endpoint.

boolean queue(ByteBuffer buffer)

Queues the request to send or receive data on its endpoint.

boolean queue(ByteBuffer buffer, int length)

This method was deprecated in API level 26. Use queue(ByteBuffer) instead.

void setClientData(Object data)

Sets the client data for the request.

Protected methods

void finalize()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

Inherited methods

Public constructors

UsbRequest

added in API level 12
public UsbRequest ()

Public methods

cancel

added in API level 12
public boolean cancel ()

Cancels a pending queue operation.

Returns
boolean true if cancelling succeeded

close

added in API level 12
public void close ()

Releases all resources related to this request.

getClientData

added in API level 12
public Object getClientData ()

Returns the client data for the request. This can be used in conjunction with setClientData(Object) to associate another object with this request, which can be useful for maintaining state between calls to queue(ByteBuffer) and UsbDeviceConnection.requestWait()

Returns
Object the client data for the request

getEndpoint

added in API level 12
public UsbEndpoint getEndpoint ()

Returns the endpoint for the request, or null if the request is not opened.

Returns
UsbEndpoint the request's endpoint

initialize

added in API level 12
public boolean initialize (UsbDeviceConnection connection, 
                UsbEndpoint endpoint)

Initializes the request so it can read or write data on the given endpoint. Whether the request allows reading or writing depends on the direction of the endpoint.

Parameters
connection UsbDeviceConnection

endpoint UsbEndpoint: the endpoint to be used for this request.

Returns
boolean true if the request was successfully opened.

queue

added in API level 26
public boolean queue (ByteBuffer buffer)

Queues the request to send or receive data on its endpoint.

For OUT endpoints, the remaining bytes of the buffer will be sent on the endpoint. For IN endpoints, the endpoint will attempt to fill the remaining bytes of the buffer. If the queueing operation is successful, return true. The result will be returned via UsbDeviceConnection.requestWait()

Parameters
buffer ByteBuffer: the buffer containing the bytes to send, or the buffer to fill. The state of the buffer is undefined until the request is returned by UsbDeviceConnection.requestWait(). If the request failed the buffer will be unchanged; if the request succeeded the position of the buffer is incremented by the number of bytes sent/received. Before Build.VERSION_CODES.P, a buffer of length larger than 16384 bytes would throw IllegalArgumentException. In API Build.VERSION_CODES.P and after, any size buffer is valid.

This value may be null.

Returns
boolean true if the queueing operation succeeded

queue

added in API level 12
public boolean queue (ByteBuffer buffer, 
                int length)

This method was deprecated in API level 26.
Use queue(ByteBuffer) instead.

Queues the request to send or receive data on its endpoint.

For OUT endpoints, the given buffer data will be sent on the endpoint. For IN endpoints, the endpoint will attempt to read the given number of bytes into the specified buffer. If the queueing operation is successful, return true. The result will be returned via UsbDeviceConnection.requestWait()

Parameters
buffer ByteBuffer: the buffer containing the bytes to write, or location to store the results of a read. Position and array offset will be ignored and assumed to be 0. Limit and capacity will be ignored. Once the request is processed the position will be set to the number of bytes read/written.

length int: number of bytes to read or write. Before Build.VERSION_CODES.P, a value larger than 16384 bytes would be truncated down to 16384. In API Build.VERSION_CODES.P and after, any value of length is valid.

Returns
boolean true if the queueing operation succeeded

setClientData

added in API level 12
public void setClientData (Object data)

Sets the client data for the request. This can be used in conjunction with getClientData() to associate another object with this request, which can be useful for maintaining state between calls to queue(ByteBuffer) and UsbDeviceConnection.requestWait()

Parameters
data Object: the client data for the request

Protected methods

finalize

added in API level 12
protected void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
Throwable